Bed material for bubbling fluidised bed combustion

Abstract

The invention is in the technical field of bubbling fluidized bed combustion and relates to the use of ilmenite particles with an average particle size <dp> between 0.1 mm and 1.8 mm as bed material for a bubbling fluidized bed (BFB) boiler with an excess air ratio (λ) below 1.3 and to a method for operating a bubbling fluidized bed (BFB) boiler, comprising carrying out the combustion process with a bubbling fluidized bed comprising ilmenite particles as defined in any one of claims 1 and 4 - 5 ; and setting the excess air ratio (λ) to a value below 1.3.

The invention claimed is: 
     
       1. A method, comprising:
 i) providing an amount of ilmenite particles with an average particle size between 0.1 mm and 1.8 mm as bed material in a furnace with a bubbling fluidized bed boiler, wherein the amount of ilmenite particles as a proportion of total bed mass is at least 20% by weight, and 
 ii) operating the bubbling fluidized bed boiler for combustion of biomass fuel or waste-based fuel with an excess air ratio λ, below 1.3, wherein in a single bubbling fluidized bed boiler operated under continuous conditions, the ilmenite particles exhibit a reducing-oxidizing effect utilized during the combustion. 
 
     
     
       2. The method of  claim 1 , wherein λ, is 1.25 or less. 
     
     
       3. The method of  claim 1 , wherein λ, for the combustion of waste-based fuel is 1.23 or less. 
     
     
       4. The method of  claim 1 , wherein
 i) the ilmenite particles have an average particle size
 that is at least 0.2 mm; and 
 that is not more than 1.8 mm; 
 
 and/or 
 ii) the ilmenite particles have a particle size in the range from 0.1 mm to 1.8 mm. 
 
     
     
       5. The method according to  claim 1 , characterized in that the ilmenite is crushed rock ilmenite. 
     
     
       6. A method for operating a bubbling fluidized bed boiler, comprising:
 a) carrying out a biomass fuel or waste-based fuel combustion process in a furnace with a bubbling fluidized bed comprising ilmenite particles having an average particle size between 0.1 mm and 1.8 mm wherein the amount of ilmenite particles as a proportion of total bed mass is at least 20% by weight, wherein in a single bubbling fluidized bed boiler operated under continuous conditions, the ilmenite particles exhibit a reducing-oxidizing effect utilized during the combustion process; and 
 b) setting an excess air ratio λ, in the furnace to a value below 1.3. 
 
     
     
       7. The method of  claim 6 , wherein λ, is set to 1.25 or less. 
     
     
       8. The method of  claim 6 , wherein λ, for the combustion of waste-based fuel is set to 1.23 or less. 
     
     
       9. The method of  claim 6 , wherein the bubbling fluidized bed further comprises silica sand particles, wherein
 i) the silica sand particles have a particle size in the range from 0.25 mm to 2.0 mm; and/or 
 ii) the silica sand particles have an average particle size between 0.6 mm and 0.8 mm. 
 
     
     
       10. The method of  claim 6 , wherein the amount of ilmenite particles as a proportion of the total bed mass is at least 30% by weight. 
     
     
       11. The method of  claim 6 , characterized by setting the fluidizing gas velocity to at least 0.03 m/s. 
     
     
       12. The method of  claim 6 , characterized by providing at least 50% of the combustion air as primary fluidizing air. 
     
     
       13. The method of  claim 6 , characterized by a sooting interval of at least 2 days. 
     
     
       14. The method of  claim 6 , wherein fuel and/or the ilmenite particles are continuously supplied to the bubbling fluidized bed boiler. 
     
     
       15. The method of  claim 6 , wherein the ilmenite particles are supplied to the bubbling fluidized bed boiler
 at a rate of less than 3 kg/MWh thermal output when biomass fuel is used; and 
 at a rate of less than 6 kg/MWh thermal output when waste-based fuel is used.